This disclosure relates to high definition television (HDTV) and more particularly to preventing unauthorized recording of HDTV signals.
There is a need for High Definition Television (HDTV) output signals from DVD players and other such video source devices. However, the Hollywood movie industry wants to provide copy protection on these High Definition (HD) output signals that performs the same function as the known Macrovision Corp. Anti-copy Process (ACP) present on the NTSC or PAL television output signal of virtually every DVD player now in existence. One version of the Macrovision ACP is described in U.S. Pat. No. 4,631,603.
The technical problem is conveying HDTV analog signals from a DVD player or set-top cable TV decoder box to a TV set. If the video is in the clear, it is subject to being copied by HDTV video recorders, or to being converted to NTSC or PAL TV and then being copied on conventional VHS and 8 mm video recorders. Watermarkingxe2x80x94with appropriate detection circuitry in future compliant recordersxe2x80x94has the potential to solve this recording problem to the extent that it provides a means to convey copy control information, (although it will not help with the NTSC/PAL converter problem). However, a viable watermarking technology has yet to be defined and adopted. In addition, watermarking does not address potential recording devices which are not compliant with the watermarking system; whereas, this disclosure addresses those non-compliant recording devices.
This disclosure is directed to a method and apparatus for providing simple and inexpensive yet highly secure scrambling for high-definition television analog signals, to prevent those television signals from being recorded on an unauthorized basis. In this context, xe2x80x9cpreventionxe2x80x9d is defined not as preventing recording per se, but as removing the commercial entertainment value (viewability) of any resultant recording and thus inhibiting recording. Descrambling occurs only in the display device (TV set), so that the descrambled picture may be watched (in real time) but not usefully recorded.
Because in the present scrambling method a position modulation signal is conveyed in a non-recordable manner from the DVD player or other source to the TV set, the present xe2x80x9cHigh Definition PhaseKryptxe2x80x9d (HDPK) scrambling method uses a real-time transaction between the two for descrambling. Consequently, protection against copying using off-the-shelf video recorders is inherent. In other words, even if the Y (luminance), Cr (red chrominance, equal to R-Y), and Cb (blue chrominance, equal to B-Y) components of the scrambled HDTV signal were recorded with perfect fidelity on any compatible recording device, the replayed image would be unwatchable because the crucial descrambling information would have been lost.
If the scrambled video is converted to NTSC or PAL TV using a VGA to NTSC/PAL converter, the converted signal will produce unwatchable images, again because the crucial descrambling information would be lost. If the converted signal is recorded on a VHS or 8 mm video recorder, the replayed signal will also produce unwatchable images.
Further, there is provided a special electrical interface between HDPK-compliant source devices (e.g., a DVD player or set top decoder box) and the HDTV set by which an end-of-frame (or other location) decoding pulse of the HDPK signal is rendered xe2x80x9cinvisiblexe2x80x9d to standard recording devices. This interface behaves likexe2x80x94and indeed it isxe2x80x94a standard 1 volt 75 ohm video interface at all times except for the few microseconds prior to the beginning of each vertical blanking interval when the decoding pulse is being transmitted.
This disclosure also describes how to permit recording of video signals scrambled using the HDPK video security process. Note that practice of such techniques to record copyrighted material would likely violate criminal provisions of the Digital Millennium Copyright Act.